I've come up with a short list of miscellaneous facts about 401(k) plans that are not so commonly known. As always, I'm not an expert, so you might want to contact a tax professional for clarification.
1) Company stock: when you take a distribution, you can take a distribution of stock shares, and pay ordinary income tax on your cost basis. You can hold these shares outside of the 401(k) until you sell your company stock shares. You will then pay taxes only at the lower capital gains rate on the amount gained.
2) 401(k) plans are qualified plans that afford you greater legal protections than a rollover IRA. Of course, this only comes into play only if you are sued later in life.
3) 401(k) plans have a fiduciary duty to invest your money. What this means is that the 401(k) administrators need to select appropriate investment choices for you. This is not the case with an IRA.
4) Contributions to 401(k) plans are indexed to inflation beginning in 2007. In 2001, Congress passed the Economic Growth and Tax Relief Reconciliation Act that set forth a schedule for the increases in 401(k) contribution limits. Through 2006, this was $1000 per year. From 2007 onward, the contributions are indexed to inflation (known as a cost-of-living adjustment) rounded to $500 increments. The small increase for this year is because the inflation rate is low. For 2007, the current contribution limit is $15,500.
5) In-service distributions: You don't need to quit your job in order roll money from your 401(k) into an IRA. Companies don't advertise this fact, but in most cases you can request an "in-service distribution" and roll that into an IRA while you are still working there. You will need to read through the company 401(k) plan documents to find the details for your plan.